feat: add tool metadata in FastMCP.tool decorator

[mat-octave]

Adds a feature to add metadata to a tool using the FastMCP.tool decorator, passing it to the Tool object.

Motivation and Context

ChatGPT's App SDK expects information about UI resources to be in a tool's _meta field. The decorator FastMCP.tool didn't accept metadata but the field exists on the lower-level mcp.Tool object.

How Has This Been Tested?

I added metadata to mcp.tool(...) and started the server successfully. I used the Model Inspector to list the tools, and the metadata was visible in the schema.

Breaking Changes

No, this just adds an optional field meta.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

[maxisbey]

Thanks for the submission @mat-octave ! I've gone ahead and pushed a unit test to your branch as well so we can get this merged :)

[saqadri]

@maxisbey can we get a minor bump for the package published to pypi with these changes? Thank you! And thanks @mat-octave for fixing this!

[felixweinberger]

@maxisbey can we get a minor bump for the package published to pypi with these changes? Thank you! And thanks @mat-octave for fixing this!

We generally do releases on Thursdays, so this will be in there on 10/23

[saqadri]

@maxisbey can we get a minor bump for the package published to pypi with these changes? Thank you! And thanks @mat-octave for fixing this!

We generally do releases on Thursdays, so this will be in there on 10/23

Perfect, thank you @felixweinberger!

[juanlarrambebere]

Hi! Very eager to try this release as well!